cabal file adjustments

1 files changed, 11 insertions, 1 deletions

diff --git a/TraversableT.hs b/TraversableT.hs
index 98a97bf6..cc187951 100644
--- a/TraversableT.hs
+++ b/TraversableT.hs
@@ -4,7 +4,7 @@ import Data.Traversable
 import Control.Monad (join,MonadPlus(..))
 import Control.Monad.Trans.Class
 import Control.Applicative
-import Data.Foldable (Foldable(foldMap))
+import Data.Foldable (Foldable(foldMap), toList)
 import Data.Maybe (maybeToList)
 
 -- | 
@@ -82,3 +82,13 @@ liftMaybe = liftT . maybeToList
 liftIOMaybe :: IO (Maybe a) -> TraversableT [] IO a
 liftIOMaybe = liftMT . fmap maybeToList
 
+handleT :: ( Monad m
+           , Traversable t ) =>
+        (t a -> TraversableT t m a)
+        -> TraversableT t m a
+        -> TraversableT t m a
+handleT catcher body = TraversableT $ do
+    tx <- runTraversableT body
+    if null (toList tx)
+        then runTraversableT $ catcher tx
+        else return tx